marvnero
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Joined: February 2017
Posts: 33
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Post by marvnero on Dec 17, 2017 12:07:33 GMT -5
Hi John, I'm building an annular combustor. The picture is showing the inner ring of the combustor. The current setup with the cone is used to feed a turbocharger. If the combustor works like it should, I'd like to build a more compact gasturbine with a layout similar to your and Anders turbines. The current configuration is only used to test the combustor with a Turbocharger. I drew some very ugly arrows on the combustor's drawing, but I hope it will delete your concerns on my design: postimg.org/image/6aid1g4kn/Please let me know if you still have any doubts about my concept, so I can improve it before wasting more time and being disappointed about a none working pile of scrap metal at the end. Cheers, Marvin
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Post by racket on Dec 17, 2017 15:03:23 GMT -5
Hi Marvin
Thats more like it , making sense now :-)
Have you considered having an inlet hole in the cone baffle at the Primary end so that the air doesn't have to make such abrupt changes in direction around the baffle to get into the inner wall holes , perhaps have the hole area roughly the same as the inner wall holes total area
Cheers John
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marvnero
Member
Joined: February 2017
Posts: 33
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Post by marvnero on Jan 2, 2018 17:40:35 GMT -5
Hi John, Yes, there is a hole in the cone baffle to avoid stopping the air too abruptly. The hole is currently rather small as I wanted to avoid a higher absolute pressure in the inner flametube. Your idea to use a hole of the same area as the total hole area of the inner flametube makes sense though. Do you think that the slightly higher absolute pressure in the inner flametube doesn't matter that much? Luckily i didn't roll the cone baffle yet The outer shell however is finished. I got some contaminants in the seams, but they should be gas tight. Thanks to Anders rolling device the outer shell looks far better than I expected. Gallery of the outer shell: postimg.org/gallery/1d4mkf1k6/PS: Happy new year to everyone !! Cheers, Marvin
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Post by racket on Jan 2, 2018 22:26:12 GMT -5
Hi Marvin
As long as the delivery tube to the combustor is fairly large with relatively low air speeds ( <100 m/s )there won't be a lot of dynamic pressure , I wouldn't be concerned .
Cheers John
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marvnero
Member
Joined: February 2017
Posts: 33
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Post by marvnero on Jan 4, 2018 6:17:24 GMT -5
Hi John,
In a rough estimation the velocity of the air entering the outer shell should be well below 100 m/s. I'll increase the center hole area of the cone baffle. The whole idea of the cone baffle was to create a dump diffuser. As the air speed is already very low (should be below 20 m/s), I'd guess there's no diffuser needed. Using the cone to have less turbulence in the air flowing to the outer ring of the combustor doesn't seem to be a disadvantage though...
Cheers, Marvin
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Post by racket on Jan 4, 2018 17:30:07 GMT -5
Hi Marvin
Yep , keep the cone to direct the flow to the outer wall , the gap between the cone and flametube end will tend to equalise pressures between the inner and outer walls if there is any slight difference in pressure from the air entering axially through the centre hole in the cone .
Cheers John
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marvnero
Member
Joined: February 2017
Posts: 33
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Post by marvnero on Jan 24, 2018 19:38:53 GMT -5
Hi folks, Here's yet another update on my build! I finished the front part of the flametube today. The only thing missing is the cone baffle, but it'll be attached soon. I tried bending the frontcover utilizing the wooden plates I machined some time ago and my 90kg of pure manliness to shape it like a donut halfcut. That worked surprisingly well...until I began welding it to the flametubes. It warped so badly that I had to bash it flat again to get a somewhat gas tight weld and the inner ft kind of centered. Does anyone know how to bend something without having it warp terribly while welding it? You'll find pictures of the bent cover as well as the horrible looking, yet finished combustor in the gallery linked below. john thanks for your ongoing support an time wasted on my growing pile of scrap metal! PS: welding that 0.8mm sheet metal was a pain in the ass...please don't judge my welding skills I know the result looks like an ape had fun using a TIG welder... postimg.org/gallery/i8x1uyee/Cheers, Marvin
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marvnero
Member
Joined: February 2017
Posts: 33
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Post by marvnero on Feb 18, 2018 9:10:33 GMT -5
Hi folks, The building process of my combustor is pretty close to be completed. The only parts still missing are the fuelinjectors and the propane preheating system. Fabricating a Backplate to connect the Turbocharger to the combustor wasn't that easy as I couldn't use a waterjet cutter. I'd like to shortly describe how to achieve a round cutout in thick sheet metal without any high-tech equipment. 1) use a small drillbit and create a line of holes following the contour of your cutout. 2) use an old chisel (preferably with a hardened tip) and chisel away the left over material on both sides of the part. You don't have to break through completely. 3) place your part on a vice or something else to support the part everywhere but where the cutout is. 4) hit it with a hammer to break is loose. 5) file away any excessive material. This method may not produce a perfect finish but if you have to get the job done without any high tech cutter, it is acceptable in my opinion. It works best with mild steel or softer materials. You can find photos of the different stages in the gallery linked below. postimg.org/gallery/2afr8yeti/
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Post by racket on Feb 18, 2018 16:01:44 GMT -5
Hi Marvin
Yep , standard "low tech" method , LOL.............how we all had to do it once , and still do on occasion , a good sharp chisel can work wonders :-)
Cheers John
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Post by madrocketscientist on Feb 18, 2018 23:36:20 GMT -5
Marvin, You may or may not find the following useful I do the similar thing since my brother sold his mill drill, but I start with smaller pilot holes(say 3mm) and then a larger (say 8mm) drill bit. If the pilot holes are placed carefully the larger holes slightly overlap or are right next to each other. If you are careful with the drill, the pilot hole keeps the drill bit straight and stops it wandering into the hole beside it. I tend to leave 3 or 4 points around the perimeter to hold the cutout piece in place. The tabs can then be knocked out with a chisel or BBH. I finish the hole up with a die grinder and file. It really is amazing what one can do with limited tools and a bit of ingenuity, keep those updates coming! Shannon.
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marvnero
Member
Joined: February 2017
Posts: 33
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Post by marvnero on Jul 22, 2019 10:28:05 GMT -5
After over a year of no activity (did an internship and had to finish my B.Sc.), I'm finally back with a huge update on my build! It took me quite some time to figure out how I'd like to design and build my fuel system. I decided to build a Kamps-style fuelsystem. I did CFD calculations on the fuelsystem to figure out the right dimensions to ensure a sufficient fuel flow and equal distribution between the 8 evaporators, because my turbine will be way more powerful than the Kamps turbine. After figuring out the dimensions of the fuel system, I decided to use copper pipe and brass needles instead of stainless steel, because I had no tools to bend a stainless steel fuel ring and I thought that brass would be a better match to solder it to the copper fuel ring. I checked the flow through all the needles using water afterwards and the flow seemed to be pretty similar between the needles. Looks like using CFD simulations was worth the effort The next step will be testing the combustor and the fuelsystem with a quite powerful leafblower. I still have to figure out what size the orifice at the combustor outlet has to have to get similar velocities as there will be later, when the combustor is fed by the actual compressor. I'll base those calculations on Mach equality to maintain same Mach numbers i the combustor during the leafblower test compared to the actual operation with the compressor. For this initial test I'm planning to simply ignite the propane mixture at the outlet of the combustor. Is there any reason why that should not work it my case? Later on I'll put a sparkplug into the primary zone, but right now I'm still waiting for some high voltage components I ordered in china. Cheers, Marvin PS: I attached some images of a quick mock-up
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